1. The Field of the Invention
This invention relates generally to digital communication systems employing parallel interfaces. More particularly, the invention relates to interfacing parallelly interfaced devices through a restricted or minimal bus architecture.
2. Present State of the Art
Traditional digital data systems, such as computers and modems, utilize a bus architecture for interfacing components with one another. In one example, a personal computer employs a computer bus, such as an Industry Standard Architecture (ISA), to define a standard parallel bus architecture onto which devices, such as microprocessors and memory devices, are connected to facilitate a data highway over which data may be exchanged with other components. Such bus architectures have employed parallel bus implementations to enhance the data throughput capability required in exchanging high-data rate information.
Likewise, peripheral modules such as modems also employ similar bus architectures for interfacing the microcontroller with other support devices such as a digital signal processor or other parallelly interfacable components such as memories and I/O support devices. For example, FIG. 1 illustrates a prior art depiction of a host 18 which may take the form of a personal computer interfacing via a bus architecture, such as ISA, PCI, PCMCIA or others, to a peripheral device such as a modem 12. Such devices couple via a connector 16 generally supporting yet a parallel interface with host 18. The electronics of such an interface are illustrated as interface 20 wherein timing, signalling, drive levels and other required interface signal conditions required by host 18 are implemented for compatible communication between host 18 and modem 12.
Modem 12, in a traditional role, couples to a public switched telephone network (PSTN) 10 to provide routing for modulated data generated or consumed by host personal computer 18. A controller 22 controls or facilitates the exchange of data between a digital signal processor 28 providing modulation of digitized data with host 18. A CODEC 30 performs traditional analog-to-digital and digital-to-analog conversion between the digital and analog domains, while a DAA 32 implements an isolation boundary thereby providing protection and safety between host 18 and PSTN 10. Such an implementation further employs an interface 14, generally consisting of an RJ-11 interconnection to the tip and ring signals associated with PSTN 10.
Such a traditional modem implementation provided an interface with PSTN 10 for implementing a traditional data propagation path capable of the sustained bandwidth levels associated with PSTN 10. As modem 12 came to be employed in other applications other than the physical cabling of host 18 with PSTN 10, additional functionality was incorporated within modem 12. For example, many modern modems may be employed to exchange data over modern communication channels such as wireless communication channels. In such an embodiment, the transmit and receive data are exchanged with a wireless transceiver such as a cellular telephone through a digital interface resident to the wireless transceiver. Such a digital interface with the wireless transceiver requires the development of a shared interface 34 providing such interface signals such as data in, data out, clock, and other signaling conduits as required by the digital interface of wireless transceivers. Such additional functionality requires that a significant number of contact pins be resident within shared interface 34 for an operable interconnection with a peripheral device such as wireless transceiver.
While physically larger implementations of modem 12 are more accommodating for the growth of shared interface 34 resulting from increased incorporation of functionality within modem 12, modern and miniaturized integrated versions of modem 12, such as PCMCIA implementations, contain physical size restraints on the size and pin-count associated with shared interface 34.
Furthermore, yet more modern implementations of modem 12 incorporate improved digital exchange technology, such as is associated with the Integrated Services Digital Network (ISDN) which provides improved bandwidth for data exchanges. Referring to FIG. 1, an ISDN network 36 requires specific signaling from modem 12 for compatible interface therewith. Integration of such enhanced technology within modem 12 requires the integration of an ISDN-specific I/O device 26 for performing such required signaling standards. Interfacing of ISDN signals from modem 12 with ISDN network 36 requires the routing of such signals through shared interface 34. Such routing of signals through shared interface 34 further consumes a portion of any residual pins associated with shared interface 34 in a form factor-restricted implementation of modem 12 such as in the case of a PCMCIA or other integrated peripheral implementation.
For efficiency and bandwidth concerns, ISDN-specific I/O device 26 employs a parallel interface with controller 22 via an ISDN interface 24. Such a parallel interface facilitates enhanced data rate exchanges between DSP 28 and ISDN-specific I/O device 26.
While such a prior art implementation of the embodiment illustrated in FIG. 1 depicts the incorporation of ISDN-specific I/O device 26 within the form-factor associated with modem 12, other implementations of modems prefer the placement of ISDN-specific I/O device 26 external to modem 12. Such an embodiment is beneficial in applications wherein the integration of ISDN-specific I/O device 26 within the physical confines of modem 12 would violate size or design constraints placed upon modem 12. In such implementations, ISDN-specific I/O device 26 is better placed in yet an external module or podule separate and external to modem 12. While such an implementation may meet the timing and signaling conditions as required by ISDN network 36, the standard modem interface associated with ISDN-specific I/O device 26 employs a parallel interface with controller 22 and DSP 28. In an embodiment incorporating the external placement of ISDN-specific I/O device 26, such routing of the parallel interface further consumes vacant pins associated with shared interface 34. In fact, in physically limited implementations of modem 12, such as in PCMCIA, shared interface 34 may be physically unable to accommodate all of the parallel interface lines therethrough. While external placement of ISDN-specific I/O device 26 may provide economic integration benefits, external placement of a parallelly interfaced device such as ISDN-specific I/O device 26 outside the physical bounds of modem 12 may be physically prohibitive if the entire parallel interface is incapable of being routed through restricted shared interface 34.
Thus, what is needed is a method and system for interfacing parallelly interfaced devices through a restricted path interface. Furthermore, what is desired is a method and system for interfacing parallelly interfaced devices via a restricted path conduit without incurring significant throughput performance degradation.